advancements in modern startle response systems
TRANSCRIPT
Advancements in Modern Startle Response Systems
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Advancements in Startle Reflex: An in-depth discussion on piezo/Plexiglas sensors versus load cell sensors
Michael Kinder
President, CEO
Kinder Scientific Company
VP Business Development
OtoScience Labs
Copyright 2015 Michael Kinder, Kinder Scientific and InsideScientific. All rights reserved.
Thank you to our event sponsor
Open Field
Cage Rack
Pulse Maze
Rotometer
Light / Dark
Startle Reflex
Forced Swim
Active / Passive Avoidance
Tail Suspension
Cue and Contextual Fear Conditioning
Place Preference
Learning Hole board
Kinder Scientific - Behavioral System Core
Today’s discussion
1. A history of piezo/Plexiglas sensing assemblies and why it’s time to move on: • What does it actually measure
• Is it a true accelerometer?
• Strengths & Weaknesses of the design
2. The applicability of Load Cell sensors: • Strengths &Weaknesses
The high speed videos in this presentation have been provided by:
Alexander Galazyuk, Ph.D.
Associate Professor Department of Anatomy & Neurobiology
Northeast Ohio Medical University
We are very grateful for Alex’s generosity and stunning quality
of work that he and Ryan Longenecker demonstrated in the creation of these videos.
What measure are we after ?
A Whole Body Reflex from a loud noise!
For over 20 years the piezo/Plexiglas sensing assembly was the dominant method for measuring startle responses Much of the science on startle reflex stands on the shoulders of this technique.
How the piezo/Plexiglas sensor works
Spring alone (no energy)
Subject’s mass Subject’s mass + Response
• Because the Plexiglas plate is a spring, the signal coming off the piezo necessarily contains the spring characteristics
• This adds significant and sometimes confounding complexity to analyzing the data
• The design requires some method of centering the subjects downward force over the piezo
• It is important to understand that the piezo is the transducer, not the sensor. The entire assembly is the sensor (or sensor assembly)
How the piezo/Plexiglas sensor works
Piezo glued to plate and sealed
Platform legs Plexiglas plate
Subject reflex response
• Animal mass preloads the spring of the Plexiglas plate
• Think if this as stored energy what will be released back into the data
How the piezo/Plexiglas sensor works
Plexiglas/Piezo Sensor
Animal Mass
• When the animal startles, the Plexiglas spring is now loaded with the animal mass + the startle response
• This is why the second positive peak can be larger than the first
How the piezo/Plexiglas sensor works
Subject reflex response bends the plate
Plexiglas/Piezo Sensor
Early Waveforms…25 years ago
Graph of – 115d20msHabit @ Trial 8
• This early approach provides only the absolute values and makes it very difficult to know what is actually happening from a study of the waveform.
Early Improvements to Full Wave Signal!
Graph of – 115d20msHabit @ Trial 8 • This is the exact
animal data from the previous slide.
• It is clear that the “spring” is oscillating
• And the sensing assembly is not faithfully following the animal response
• What does the output of the sensing assembly actually represent?
– The combination of the response and the spring!
• Is it truly an accelerometer?
– No! this is a misnomer. It is more of a kinetic energy measurement.
• Does the animal weight matter?
– Yes! Dampens Spring
• Can it be properly calibrated?
– Possibly, but with great difficulty.
Has the piezo/Plexiglas sensor outlived its usefulness?
Calibrating the piezo/Plexiglas sensor – or is it only equilibrating? • The piezo transducer produces a DC voltage analogous to the
amount of bend it experiences.
• However, because it bleeds off the signal so quickly, it only outputs a value when the plate is in motion. Likely here is where some of the confusion over being an accelerometer. But the voltage it creates is not analogous to acceleration but instead change in
distance (bend).
• Calibration - verb (used with object), calibrated, calibrating. 1. to determine, check, or rectify the graduation of (any instrument giving quantitative measurements).
• Because we are trying to measure the force exuded by the animal, “calibrating” in volts is not actually calibrating. The best we can hope for in this approach is “equilibration”, i.e., making the sensors from multiple stations produce the same output value for a known input force.
Equilibrating
Equilibrating the piezo/Plexiglas sensor with an eccentric vibrating motor
Challenges & weaknesses with an eccentric vibrating motor
1. The frequency difference between the Plexiglas plate and the revolutions of the motor cause inconsistent forces to occur. They beat against each other.
2. Makes it difficult to calibrate to a standard unit of force such as Newton.
3. Because the animal weight has a significant effect on the spring characteristics of the sensor, one would need a calibrator for each animal weight equal to the animal weight. Therefore, it is not practical to pursue true calibration, but rather, accept equilibration as the goal.
4. It is difficult to prove linearity
1. We are stuck with using arbitrary units such as volts or just a number or…
2. We can link the performance of the plate to a Newton with a single pulse solenoid that is calibrated on a NIST traceable apparatus. Still, this does not accurately tie the unit of measure to Newton because of the effect of the animal weight.
3. This is why you should not compare raw amplitudes of different weight animals, or even the same animal at different ages when using a piezo/Plexiglas sensing assembly. Not apples and apples, but rather apples and oranges.
Piezo/Plexiglas Sensors…
Moving to the next level
Load Cell Sensor Assembly
Strengths:
• Faithfully follows the animal response
• Easy static calibration with fixed weights (easily made NIST traceable)
• Easy to prove linearity
• Ability to compare responses of different weight subjects
Weaknesses:
• More expensive to manufacture
Load Cell Sensor
Faithfully follows
response
Post Session Trial Retrace with Load Cell Sensor
• Note the response from the system is very similar to the video. The negative peak is a result of the mass of the restrainer
0.0
4.0N
It’s about the data!
The Purpose of Nostim Trials
Is this the right question?
What is the purpose of Nostim (no stimulus) trials?
What was the subject doing during these times?
• What was the subject doing just prior to startle elicitation?
• That is what should determine the validity of the trial.
Evaluating pretrial activity
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8.0N
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8.0N
Dual Analysis Windows
• Each trial can be automatically evaluated for pre-startle activity?
Window A Window B
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Dual Analysis Windows
Window A
1. Determine True Pre-startle activity in the first window
2. Accurately set the second window for the first positive response
Window B
Final Thoughts
• Dr. Alexander Galazyuk’s publication in the Journal of Neuroscience Methods “An improved approach to separating startle data from noise”
• Pay close attention to how your system is calibrated or equilibrated and know the difference between the two. Make sure to continually convince yourself that your system is recording the same response for a known input. It is one of the most overlooked area of startle research.
• Ask yourself if comparing startle amplitudes of different size animals matters to you and decide accordingly
Thank You!
For additional information on startle response systems, sensor technologies, and best practices for calibration and protocol design, please visit:
http://www.kinderscientific.com
Michael Kinder
(858) 679-1515
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InsideScientific is an online educational environment designed
for life science researchers.
Our goal is to aid in the sharing and distribution of scientific
information regarding innovative technologies, protocols, research
tools and laboratory services.